This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/FI99/00537 which has an International filing date of Jun. 18, 1999, which designated the United States of America.
The present invention relates to a method [according to the preamble of claim 1] for controlling the interelectrode distance of micromechanical components by electrical means.
The invention also concerns a system for controlling the interelectrode distance of micromechanical components.
In many types of micromechanical components and sensors implemented by silicon techniques, a vital part is formed by an electrode structure comprising two, typically planar electrodes whose interelectrode distance is arranged variable by means of an electrostatic force. Generally, the interelectrode distance has been varied by controlling the AC or DC voltage applied over the electrodes. Herein, the control range of interelectrode distance is limited by the so-called pull-in voltage Upi. When the control voltage exceeds this value, the electrodes will hit each other under the electrostatic force pulling them together.
In the art are known methods based on driving the interelectrode distance of a moving electrode capacitor by means of controlling the DC charge imposed over the electrodes. Although this technique is capable of reducing the risk of electrode pull-in, a practicable construction thereof requires a galvanic contact to the electrodes.
It is an object of the present invention to overcome the disadvantages of the above-described techniques and to provide an entirely novel method for electrical control of interelectrode distance in micromechanically fabricated electrode structures.
The goal of the invention is achieved by virtue of controlling the interelectrode distance by virtue of controlling the level of AC current passed through the electrodes.
The invention offers significant benefits.
In addition to offering an efficient method of controlling the interelectrode distance without a risk of electrode pull-in, the novel control technique can be implemented in a capacitive or inductive manner without a galvanic contact. Particularly in silicon micromechanical constructions, this control technique can provide significant benefits, since the fabrication of any galvanic control signal contacts to electrodes tends to complicate a micromechanical construction beyond the limits of acceptable production cost efficiency.
Advantageous applications of the invention can be found in new silicon micromechanical voltage transfer standards and Fabry-Perot interferometers in which the control span of the interelectrode distance can be increased up to three-fold as compared to the conventional voltage control technique.
Moreover, embodiments of the invention equipped with tuned circuits according to the invention can offer a significantly boost toward a high efficiency of control.